Mystery Message – Naval Enigma?


The ciphertext message below we have received from John Harper and John Borthwick of the Bombe Rebuild Project. After Scharnhorst’s Last Message broke I asked John Harper if they would have any more German Naval ciphertext messages and a few days later John Borthwick sent me the message below.

Here is John Borthwick’s E-Mail accompanying the message:

Hello Frode,
 
John Harper mentioned that you're looking for more messages to break.  Attached is a 
copy of a naval message which has been on the copy-holder of the Typex machine which 
we have on display at BP.  It has been there for years as you can see from the different 
fading of the paper.  We know absolutely nothing about it other than it is obviously 
Naval since it's in groups of 4 and the indicators are repeated at the end.
 
Have fun!
 
Regards,
John

Ciphertext


BP Teleprint

STNX 10-03-43 1031 5088 28 SF283 A236 C DE 36/RTC (0430) 154= NJGH DRFU= DTHY HYSR CGNH DEJL AVZO SHUN WLKN OPRT KIDT VHWL APUT DRTW KPWK DUNC AMFR TYWM OKHY ABGT JNDE RTMO PLCR BTRA UNCE KYNC WUIN UIOP NGTC RTAZ QPMB RSAB DHIL WBCU OPBG RTDV WRSN ERTC JKWA YHJI NK = NJGH DRFU= ALT 2/7 AMGR SENT 1200 Z GHK


Facsimile of the BP Teleprinter Message (PDF format)

At the very first moment I accepted it as a German Naval Enigma message. It is in groups of 4-letters and the two 4-letter indicator groups are repeated at the end. But looking closer at it I am no longer so sure. First of all the indicator groups stands apart from the message. They are not even counted in the number of groups the message contains. And the last ciphertext group is not full; it has only two letter instead of four. I therefore think that the message needs more research before it can be attacked. One possible origin could be that it is an Abwehr message enciphered on the Enigma-G machine, the so-called Abwehr Enigma. Abwehr usually transmitted their ciphertext messages in groups of five, but in some cases they also used 4-letter groups. The two indicator groups could fit with the indicators used with the Abwehr machine. Or it could be from an Enigma-K machine, which was used by the German Railway, the Abwehr and for other special purposes. This machine would also need 4-letter indicators as the reflector (UKW) was settable. But there are perhaps other possibilities.

At NARA, in RG 457 – The NSA Historical Collection, there is a document with the title “Study of Customary Practices of German Radio Procedure, 1944,” Nr. 1677, CBKJ21, Box 622, which describes a message like the one above:

Four-letter messages with a key made up of two groups repeated at the beginning and end of message. This type [of] message, very much used, is machine cipher, probably Hagelin, and midget submarines are known to be provided with this system.

It is doubtful if this traffic is Hagelin. Where the author of this report got this notion is difficult to see. At this time, early 1943, only the Italian Navy were using the Hagelin machine, the C38m. It is indeed possible that their midget submarine force used this machine for their communications, but it is difficult to understand why this traffic would pass over a German radio circuit. First after Italy's surrender in September 1943 did the Italian midget submarines, the 10th MAS Flotilla, go over to the Germans and came under their command.

If we look closer at the header of this message we see that it is addressed to STNX, Station X – Bletchley Park. On the line below the intercept station has written the date and time of intercept, 11 March 1943 at 10:31 Zulu. The next number, 5088, is the intercepted frequency, 5088 kHz. Then comes the number 28, which is possibly the German radio station’s row number, followed by a serial number allocated by the intercept station to each new message, here SF283, and then finally the number for the intercept series, A236. In 1944 A236 was the series that was allocated to German Air Force (GAF) traffic being transmitting on 5088 kHz. If the same traffic was allocated to this series in 1943 is not known but it is very likely the case. Tony Sale has published a set of such messages on his Web site, Codes and Ciphers. As you can see on this page, German Air Force Messages, the header from the intercept station is almost identical including the intercepted frequency. These messages are apparently enciphered with the GAF Enigma key Jaguar, the key for Luftflotte 3, but this key did not appear before in December 1944.

In the NARA document cited above there is also the following paragraph:

There is, however, one group of stations having R as the first letter of the call sign which is not organised in the aforementioned sense. These stations are apparently all aviation field stations or D/F stations for the assistance of aircraft and as a result are spread throughout all Europe and operate independently without any link.

This fits well with our understanding that this radio circuit belong to or pass traffic for the German Air Force.

By studying Ralph Erskin’s notes on Breaking Naval Enigma (Dolphin and Shark) and The Kenngruppenbuch Indicator System, and the Enigma Manuals The Enigma General Procedure and The Enigma Offizier and Staff Procedure, you will get a better feeling for the German Naval Enigma messages.

Acknowledgments

We should like to thank the Bombe Rebuild Team who, as always, is very supportive when we ask for help. In this case we should like to particularly thank John Harper and John Borthwick, who sent us the copy of the BP teleprint with the mystery message.

Further Information